In current wireless communication systems, a location request message is typically sent to a Mobile Switching Center (MSC) of the home system of the mobile unit when a call arrives for the mobile unit via an MSC's roamer access port. This requires intersystem messages to be exchanged when the home system determines that calls to that mobile unit via a roamer access port are not permitted. For example, if call terminations to a specific mobile unit registered in a visited system are prohibited, a location request message would still be initiated to the home system. Consequently, network and system resources are used unnecessarily, even when the home system has determined a priori that terminations to the mobile unit are not permitted. Further, when Wireless Intelligent Network (WIN) service applications, such as prepaid, are not part of a call (e.g. A RAN call), the potential for uncharged or fraudulent service exists.
FIG. 1 depicts a ladder diagram 100 of a call flow for denying access to a roaming mobile unit in accordance with the prior art. This method of mobile unit call restriction when roaming is done by sending a message from the serving MSC to the HLR and requesting the status of a termination restriction code field. This mechanism requires an extra SS7 message to be launched for every switch based RAN call. Consequently, the prior art method requires additional messages be sent, which can delay the start of a call for a roaming mobile unit, and consumes additional system resources.
The communication system of the prior art includes an originating system (home) MSC, a Home Location Register (HLR), a Visitor Location Register (VLR), a serving (visited) MSC, and a mobile unit. The mobile unit preferably subscribes to the originating MSC as its home system, and a subscriber record is thereby included in the HLR. In the call flow of FIG. 1, the determination of the termination access code parameter does not occur until after a call request for a mobile unit on a RAN port arrives. Therefore, the serving MSC must send a location request message asking for the status of the termination access code parameter every time a roamer port call occurs.
When traveling outside of the coverage area of the originating MSC, the mobile unit is considered to be roaming. The mobile unit can then communicate with the serving MSC, which will create a user record associated with the mobile unit and store the user record in the VLR.
Upon entering the service area covered by the serving MSC and registering, the VLR sends a registration notification message (REGNOT) 101 to the HLR. Registration notification message 101 includes the identification number of the mobile unit, as well as other parameters.
The HLR retrieves the subscriber record of the mobile unit and sends a registration notification response message 103 back to the VLR. In the prior art, the termination restriction code parameter is by default set to allow Roamer Access Number (RAN) calls to the mobile unit. This can be done by setting the value of the termination restriction code parameter to the value of “unrestricted”. The unrestricted value is the default, and therefore at this point, without further verification, calls to the mobile unit via the RAN port of the serving MSC are allowed.
A RAN call request 105 now arrives at the serving MSC for the mobile unit. The serving MSC must now determine whether the mobile unit is permitted by its originating MSC to receive RAN calls. In the prior art, this is done when a call request is received. Further, in the prior art, this is done every time a call request is received for a mobile unit utilizing a RAN port. The serving MSC must now send another message, location request message 107, to the HLR.
Location request message 107 includes, among other fields, a request for the value of the termination restriction code parameter, typically stored in the Termination Access Type field. If the termination restriction code parameter field is set to deny (RAN) calls to the mobile unit, as is indicated in FIG. 1 by the value “TerminationsDenied”, RAN call request 206 is denied and is not delivered to the mobile unit. If the termination restriction code parameter had been set to deny (RAN) calls to the mobile unit, preferably by having a value other than “TerminationsDenied”, RAN call 105 would have been delivered to the mobile unit.
Therefore, a need exists for a method and apparatus for restricting call termination when a mobile unit is roaming. Further, a need exists for a method and apparatus for restricting call termination that eliminates the chance of fraud and utilizes fewer system resources while minimizing the number of messages traversing the communication system.